This is about lobe center, what does it do,why is it important?
Lobe center is a routine, a method of fine tuning the timing of a cam, so the intake valve closes at a particular point.
The intake valve closing point is the most important valve event in the engine.
The reason? Inertia, The intake charge's momentum keeps it flowing into the cylinder despite the piston's upward movement after the intake stroke.
Delaying the intake valve's closing to take advantage of this phenomenom increases cylinder filling and thus Power. Thats a good thing.
Its kind of tricky to know just how long is enough. If the valve is held open to long the fuel charge momentum dies, gases back up up in the port suck mixture out of the cyilinder causing a loss of horse power.
If the intake valve closes to early we have limited how full the cylinder gets and horse power is lost. Either way the motor loses horse power.
The ideal thing is to close the intake valve at the precise millisecond the mixture loses its momentum and stops before it reverses direction,this is the whole point of degreeing cams, it is that this will put the cam in the correct position to make this all happen.
The reason we use the lobe center method is simple, Ramps. All cams have ramps, Acceleration ramps that gather up the clearences in the valve train before the valve is shot off its seat, and decereration ramps that cushion the shock of the valves closing. The problem is these ramps move the valve so slowly that determining when the valve has opened or closed is very difficult.Because of this, engine builders developed a method ignoring the ramp when measuring valve movment.
The ramp isn't there to move the valves anyway its sole purpose is to babysit the valve train Engine builders don't look at the valves movment until the valve has moved enough and is clear of the ramp That area is called is the checking height.
The problem is all ramps are not the same size, on a push rod motor the cam has huge ramps, because of the need to cushion the valve train components during open and closing.
Ramps on OHC motors are smaller because there fewer parts to deal with and not as much cushioning needed.
All motors are different they pretty much have they're own ramp and checking height, they can range fron .020 to .050 and it would be impossible to compare them as different checking heights give to very different timing conditions.
So measuring cam timing independent of engine design is what lobe centers are . Still using a checking height the lobe center approach indexes the cam on anaverage of its opening and closing points, its Center not one of those points. because no matter what the staring and stoping points the center of the cam will aways be the same.
Now with that being said, it is Not the Physical center that is being sought, its the Mathmatical Center, or the average of the cams opening and closing points. In some cams both points are the same but not in most.
So Lobe centers serve three purposes.
First, to time the intake valve at the critical closing point to make maximum horse power.
Second, it is an arbitrator in the world of high performance tuning it get everyone on the same page when talking cams, and valve timing.
Third, It gives bench racers something to talk about and sound knowledgable around the pits.
